Mean- Is the average of a group of numbers. You add all values together then divide by the total number of values.
Example:
12, 23, 34, 56, 3, 4, 22, 77, 87, 9 : The sum of this list is 327.
So you then divide 332 by 10 (the total # of values) So the Mean is 32.7.

Median- Is the value half way through the ordered data set, below and above which there lies an equal number of data values.
It is generally a good descriptive measure of the location which works well for skewed data, or data with outliers.
Example:
Data 96, 48, 27, 72, 39, 70, 7, 68, 99, 36, 95, 4, 6, 13, 34, 74, 65, 42, 28, 54, 69.
Ordered Data 4, 6, 7, 13, 27, 28, 34, 36, 39, 42, 48, 54, 65, 68, 69, 70, 72, 74, 95, 96, 99.
Median is 48, leaving ten values below and ten values above.

You can also find the Median with an even set of data.
Example:
Data 12, 4, 6, 8, 10, 3, 7, 11.
Ordered Data 3, 4, 6, 7, 8, 10, 11, 12.
So, the Median values here are 7and 8.
So, you would then take 7and 8 and add them together. Then you would take that sum and then divide it by 2 to get the Median (you divide it by 2 because you had 2 values to begin with).
7+8 = 15
15 divided by 2 = 7.5
So the Median here is 7.5!

Mode- Is the most frequently occurring value in a set of discrete data. There can be more than one mode if two or more values are equally common.
Example:
Here are the results from a test given to 9 students.

Then find the mode (most common score) So the Mode is 90.

Also in some cases a Mode does not exist.
Example:
2,3,4,5,6,7,8
Because no number is repeated there is no mode.
Example:
2, 3, 5, 7, 10, 5, 3.
In this case both 3 and 5 occur twice. Therefore, the data is bimodal.